Conventionally, an in-vehicle actuator mounted on a vehicle such as an automotive vehicle is used as, for example, a driving source for power window apparatus or sliding door opening/closing apparatus. Since this actuator is installed in a narrow space such as the inside of a door, the actuator includes a speed reduction mechanism configured to obtain large outputs and reduced in size and. In this case, as being installed inside a door, a passenger compartment, or the like, the actuator described above tends to be hardly exposed to external environments such as rain water, dust, and ultraviolet rays, and therefore an case made of aluminium is often adopted, with high priority given to light weight and so forth.
Meanwhile, a vehicle-mounted actuator may be used as a driving source of an electrically-operated brake apparatus, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2014-029193. The brake apparatus described in this Patent Document 1 includes an actuator for moving a piston provided in a cylinder of a caliper. The actuator described in the Japanese Unexamined Patent Application Publication No. 2014-029193 is provided near an undercarriage of a vehicle, installed in adverse environments and as a matter of course, the actuator is exposed to rain water, dust, and so forth and there are concerns such as a hit by a stone. Therefore, the case forming part of the actuator is formed of high-strength resin material so as to be able to obtain sufficient strength while having weather resistance.